I wrote a post on my site about this. I measured it out and found a 40 lb bag of compost equals 0.75 cubic feet. Take a look at this post. I did all the math and found a great way to measure it out.

Are you using more than just mushroom compost? You really need to mix three of four types together to get all the micro-nutrients you need.

Here is a link that might be useful: The best SFG measuring Cup

Thank you appmy.

I got a 2 cuft sack of cotton boll compost to go with the 6 40 lb sacks of mushroom compost I already had. Did not know that a person should get different kinds of compost.

Will probably get it put together next weekend.

Thanks again.

I used a compost from Maine that contained muscle shells, salmon and blueberries... I didn't realize you needed to mix up your compost and have already planted my plants.. I hope it works out ok.